And when people talking about leaving, they mean that the mass transmission stops and it continues to transmit, and mutate, among some small subset population (

And when people talking about leaving, they mean that the mass transmission stops and it continues to transmit, and mutate, among some small subset population (e.g. remote island, etc). Eventually it recurs in the main population, whether hitting people who never got it, or because it has mutated enough that prior protections don't defend against it. Which is exactly what happens with the flu and the cold. Lots of viruses, constantly mutating. So much so that when the next season comes around it's like an entirely new virus to your body.